Growth and Survival of Campylobacter fetus subsp. jejuni as a Function of Temperature and pH

The objective of this study was to determine what effect temperature and pH have on the ability of Campylobacter fetus subsp. jejuni to grow and survive. None of three strains of C. fetus subsp. jejuni could grow at 30 C and below or at 47 C and above. The optimum temperature for growth was in the range of 42 to 45 C. Only one of three strains, FRI-CF8, could grow at pH 4.9 and none could grow at pH 4.7. The optimum pH for growth was in the range of 6.5 to 7.5; however, all strains grew well at pH 5.5 to 8.0. Rate of cell death at pH 3.0 to 4.5 was temperature-dependent. At comparable pH, cells of C. fetus subsp. jejuni died most rapidly at 42 C, less rapidly at 25 C and at the slowest rate at 4 C. For example, at pH 4.5, a 3 log₁₀ decrease of cells occurred within 8 h when incubated at 42 C but took 4 days when incubated at 4 C. At 25 C and pH 4.5, cells were inactivated at an intermediate rate. Rates of thermal inactivation of five strains of C. fetus subsp. jejuni were determined at 48, 50, 53, and 55 C in a skim milk heating menstruum. At 48 C, D-values ranged from 7.2 to 12.8 min while at 55 C they ranged from 0.74 to 1.00 min. The times and temperatures used to pasteurize milk should be sufficient to free milk of even unusually large numbers of viable cells of C. fetus subsp. jejuni.